There are many devices where it is desired to dispense a fluid, and typically a liquid, at a low flow rate, and where it is often difficult to determine whether or not flow is occurring in a delivery conduit. Many of these applications are in the medical arena typified by the liquid dispenser described in our own International Patent Application PCT/AU02/01499 which supplies fluid for medical infusion at controlled low flow rates.
In such situations, it is important for the patient or the carer to be able to determine that flow has been established initially, and is continuing over the desired period of treatment. This has been difficult to establish in the past, particularly in low cost “disposable” types of apparatus and it has been common for patients or carers to simply revert to an observation of the amount of fluid contained in the supply reservoir from time to time to check that flow delivery is occurring. In most instances it would take several hours to observe a discernable change in the volume, in other instances it is not possible at all. In many instances this is quite unsatisfactory as the observations are difficult, and can result in heightened anxiety for the patient or the carer, and in extreme situations medical complications arising from a lack of flow over a period of time until the situation is able to be determined.
It is also desirable in such devices to provide a flow regulator which will deliver the fluid at a controlled predetermined flow rate without complication or the necessity to set parameters by the patient or carer.
There are many other applications, including non-medical applications such as the delivery of lubricating fluids to machinery or the dosing of small amounts of chemicals, where it is desirable to be able to monitor the fact that low flow rates are occurring by simple observation, and by the provision of inexpensive flow monitoring equipment.